This invention relates generally to hydrodynamic seals and more particularly to seals having hydrodynamic grooves formed therein.
Hydrodynamic shaft seals are conventionally made by molding, embossing or cutting a spiral groove or other hydrodynamic structure or aid into the seal. The hydrodynamic groove interacts with a rotating shaft to pump any lubricating oil that may find its way under the seal back to the oil side of the seal.
Hydrodynamic aids may take the form of an open spiraling channel as illustrated in U.S. Pat. No. 6,168,164, assigned to the assignee of this application, and the disclosure of which is incorporated herein by reference. Open spiraling channels have a large pumping capacity due to the relatively large fluid volume capacity they provide. However, there is a practical upper limit to the size of such open channels. Making them too large in an effort to increase flexibility can impair the static sealing capabilities and/or lead to excessive hydrodynamic pumping action, both of which are detrimental to the performance of the seal. Making the channel too large may also increase the likelihood of leakage of oil under certain conditions.
In accordance with a preferred embodiment of the present invention, a spiral hydrodynamic channel is formed in the seal wherein successive turns of the channel are of progressively diminishing volume, with the larger volume regions near the oil side of the seal and the smaller volume regions near the air side. By diminishing the volume toward the air side, the static sealing properties of the seal are improved, preventing the leakage of oil under conditions when the shaft is not rotating and/or under conditions where the housing is lightly pressurized. The larger volume regions near the oil side accommodate a greater volume of oil and thus provide an enhanced dynamic pumping effect during rotation of the shaft.
The invention also includes a method of forming a hydrodynamic channel in a shaft seal by forming a spiral first cut in a surface of the seal, and forming a second cut adjacent to the first cut to produce a spiral channel, wherein the second cut has a smaller lead than the first cut so that the channel thus formed is of progressively diminishing volume along its length.
As an alternative, the spiral channel may have one or more turns of a relatively large volume near the oil side, and a turn or turns or even a partial turn of smaller volume near the air side. In the method of forming this alternative construction, the second cut may, after one or more turns of a relatively large volume channel are formed, be adjusted to a smaller lead such that the channel becomes smaller in volume.
It is an object of the present invention to provide a hydrodynamic seal and method of manufacture having the foregoing features and capabilities.
Other objects, features and advantages of the invention will become more apparent as the following description proceeds, especially when considered with the accompanying drawings.